Signal repeaters have many applications, among which is as an electronic countermeasure. Such a countermeasure retransmits delayed pulses of a hostile radar at the same frequency, pulse repetition interval, and pulse width, back towards the radar. The hostile radar perceives these repeated pulses as authentic targets, obscuring the real target in a multitude of false echoes.
A problem arises when these repeaters are used in environments which have strong interfering signals, such as from jammers and fire control systems. These clutter signals will saturate or capture the repeater, effectively disabling it. Current repeater countermeasure systems use two techniques for operating in dense or interfering environments. Reducing the sensitivity of the repeater also reduces the clutter below the repeater's threshold. But this may also reduce the threat signal from the hostile radar below the repeater's threshold also. Another approach uses a serial chain of tunable notch filters at the repeater's input antenna, which attenuate undesired frequencies. The repeater is then insensitive to threat signals in the notched segment of the repeater bandwidth. These filters are set to remove frequencies that typically appear in interfering environments. But each filter adds significant loss to the received signals. The penalty for this technique is reduced bandwidth and dynamic range.